LONDON  Scientists in Australia have found a new species of hobbit-sized humans who lived about 18,000 years ago on an Indonesian island in a discovery that adds another piece to the complex puzzle of human evolution.

The partial skeleton of Homo floresiensis, found in a cave on the island of Flores, is of an adult female that was a meter (3 feet) tall, had a chimpanzee-sized brain, and was substantially different from modern humans.

It shared the isolated island to the east of Java with miniature elephants and Komodo dragons. The creature walked upright, probably evolved into its dwarf size because of environmental conditions, and coexisted with modern humans in the region for thousands of years.

"It is an extraordinarily important find," Professor Chris Stringer, of the Natural History Museum in London, told a news conference on Wednesday. "It challenges the whole idea of what it is that makes us human."

Peter Brown of the University of New England in Armidale, Australia, and his colleagues made the discovery of the skull and other bones and miniature tools in September 2003 while looking for records of modern human migration to Asia. They reported the finding in the science journal Nature.

"Finding these hominins on an isolated island in Asia, and with elements of modern human behavior in tool-making and hunting, is truly remarkable and could not have been predicted by previous discoveries," Brown said in a statement.

Local legends tell of hobbitlike creatures existing on islands long ago, but there has been no evidence of them.

Descendent of Homo Erectus

The hominin family tree, which includes humans and pre-humans, diverged from the chimpanzee line about 7 million years ago. Early African hominins walked upright, were small, and had tiny brains.

The new species, dubbed "Flores man," is thought to be a descendent of Homo erectus, which had a large brain, was full-sized, and spread out from Africa to Asia about 2 million years ago.

The new species became isolated on Flores and evolved into its dwarf form to conform with conditions, such as food shortages. Flores, which was probably never connected to the mainland, was home to a variety of exotic creatures, including a dwarf form of the primitive elephant Stegodon.

Modern humans had reached Australia about 45,000 years ago, but they may not have passed through Flores. The scientists suspect the new species became extinct after a massive volcanic eruption on the island about 12,000 years ago.

Brown and his colleagues have found the remains of seven other dwarf individuals at the same site since the first find.

"The other individuals all show similar characteristics and (came from) a time range that now extends from as long ago as 95,000 years to as recently as 13,000 years ago  a population of hobbits that seemed to disappear at about the same time as the pygmy elephants that they hunted," said Bert Roberts, one of the authors of the Nature study.